Recently, with the increase in the amount of power consumption and the accelerated advancement of automated industrial equipments, such as it has been annually brought out in the data communication fields, it is necessary to supply a reliable power source to the equipment. As a result, the stability of the power for the growing high-tech industries is the most imperative factor to operate the power equipments without interruption. Numerous attempts have been made to study an insulation diagnosis for the stator windings of generator in order to avoid impact of unscheduled outages in a high powered system due to insulation failures and to establish a reliable schedule in maintenance and repair thereof. The most frequently used technique in the art is an analysis and diagnosis method for the state of insulation which is performed by measuring and analyzing the partial discharge, which most effectively represents the local degradation state of the insulation concerned. The partial discharge described above is a phenomenon occurring at a portion, to which the high voltage is applied, in high voltage power equipments or many kinds of insulators, and which generally occurs even in a normal state or environment. Especially, when the partial discharge occurs due to the aging of mechanism, the magnitude thereof will be very high, which results in insulation failures of the system. Therefore, since the partial discharge as mentioned above acts as a factor which degrades safe operation and reliability of the system due to abrupt failures of the system, it becomes the most imperative parameter to identify the modulation state thereof, which should be frequently tested in a regular manner. A test for detecting the partial discharge according to the prior art is to use a partial discharge detector or a normally used oscilloscope.
However, according to the partial discharge detector or a normally used oscilloscope as mentioned above, although it has capabilities of magnitude analysis and frequency domain analysis of the partial discharge signal in connection with the time variation, it is impossible to perform a precise measurement of the frequency characteristics and the number of partial discharge pulse signals. In addition, since the frequency bandwidth of the prior art partial discharge detector is within low frequency bandwidth of 20-300 kHz, the partial discharge measurement of the insulation can only be made after the power voltage is applied directly to the insulation, which can not eliminate external noises. Therefore, the prior art method has a drawback of the partial discharge measurement for only off-line insulation diagnosis being possible.
Therefore, in order to overcome the mentioned problem, a digital Partial Discharge Analyzer (hereinafter, referred to as "PDA") as shown in FIG. 1 has been developed. In the digital PDA, the phase angle distribution in a fixed bandwidth of the partial discharge signal is represented by a gradual measurement of the phase angle information and the number of partial discharges magnitude with respect to the normal bandwidth interval of the partial discharge. This analyzer was designed utilizing one channel analysis technique or A/D conversion method. According to the analyzer, the partial discharge measurement can be effectuated not only for a predetermined bandwidth of high frequency of 1-800 Mhz, but also in on-line state of the power equipment. Also, the magnitude, the phase angle and the number of the partial discharge pulse signals can be represented by 2- or 3-dimensional plot, preferably. In addition to the above, the external noises can also be eliminated using the difference in a signal reception time (a signal transmission time) in a differential amplifying circuit.
It is noted that since the digital PDA as shown in FIG. 1 is well known in the art, the detailed description thereof will not be made more in detail for the simplicity of the specification.
However, this technique still has a disadvantage that since the partial discharge measurement is made only to predetermined frequency components which are being preset in every product of commercial analyzers, the bandwidth of frequency being measured is limited. In addition, since the phase angle distribution in the fixed bandwidth (magnitude) of the partial discharge signal is represented by a gradual measurement of the phase angle information by a predetermined amplitude and the number of the partial discharge magnitude with respect to a normal bandwidth interval of the partial discharge, the distribution of the phase angle information and the magnitude of the partial discharge being simultaneously occurred over one period(1 cycle) of the supply voltage of 60 Hz which is applied for the measurement thereof are not represented. Moreover, this technique additionally requires an expensive, dedicated measuring equipment for use with the partial discharge measurement.
Therefore, it is an object of the present invention to overcome the above disadvantages in the prior art and provide a method for measuring a partial discharge of an insulator by measuring partial discharge pulses occurring at the insulator, such as the stator windings of generator using a Frequency Spectrum Analyzer(FSA) for diagnosis of the stator windings of generator, and then analyzing the data measured therefrom.
The preceding objects should be construed as merely presenting a few of the more pertinent features and applications of the invention. Many other beneficial results can be obtained by applying the disclosed invention in a different manner or modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to both the summary of the invention and the detailed description, below, which describe the preferred embodiment in addition to the scope of the invention defined by the claims considered in conjunction with the accompanying drawings.